Method of producing hard alloys



Sept? 1932- E. H. SCHULZ' ET AL 1,877,063

METHOD OF PRODUCI NG HARD ALLOYS Filed May 8, 1930 42 t 400 a a 0 m Q Q E 4. 36 .300 -9 u a g o carbon cohfenf lnvenforsz' E. #ermann SEA! K f bheolaa Patented Sept. 13, 1932 UNITED STATES PATENT OFFICE I ERNST HERMANN SCHULZ, OF DOR'IMUND, AND KARL LdBBECKE, OF RHEIN HAUSEN, GERMANY, ASSIGNORS TO VEREINIGTE STAHLWEBKE AKTIENGESELLSCHAFT, OF

DUSSELDORF, GERMANY METHOD OF PRODUCING HARD ALLOYS Application filed May 8, 1930, Serial N0. 450,818, and in Germany March 26, 1929.

The alloys of the stellite type i. e. those known, apart from other valuable properties a very high resistance to abrasion. For this reason they are used for manufacturing machine parts which are subjected to severe abrasive wear. Their superiority over other materials, for example alloyed steels, which are intended for the same purpose, is a generally recognized fact. Moreover, it is known that by an alteration of the pouring and cooling conditions the texture of these alloys may be influenced within certain limits. This has a certain bearing upon the properties of the finished alloys in as much as coarse grained castings are more brittle than castings having a fine-grain structure. Beyond these discoveries no influence of the pouring conditions upon the properties of the finished castings has yet been ascertained and the fact that the texture .of these alloys is completely stable and cannot be changed by any kind of heat treatment, has always been considered to be a particularly important property of these alloys.

In contradistinction thereto the inventors have found that the pouring conditions as well as a subsequent heat treatment are caable ofchanging within very wide limits especially the resistance to abrasion of these stellite-like alloys. It has been ascertained that the hi hest resistance to abrasionregularly occurred when the castingscontained graphite which, as a constituent of the texture, has heretofore been entirely unknown with stellites.

An example of the decrease in abrasion shows the drawn curve of the annexed draw- For comparison the scleroscope as well as the Brinell hardness. are given, by the dotted and dashed curves respectively. It has been found'that the abrasion decreases already with a graphite content which is incapable of impairing the hardness.

Although the presence of graphite in stellite-like alloys has in itself been an entirely novel feature, the discovery that the formation of graphite could be enhanced in a similar manner as with ordinary pig iron was still more astonishing. According to the invention a high graphite content is being obtained first, as in the case of cast iron, by greatly retarding the rate of solidification and cooling after the pouring operation by suitably controlling the casting temperature, the temperature,dimensions and composition of the mould, second by making the carbon content as high as to cause part thereof to separate out in the form of graphite even with a more rapid cooling. Experience has shown that this is the case when the carbon content amounts to more than 2%. Finally, the separation of the graphite may be brought about also in the solidified alloy by heating the pieces to a temperature of more than 7 00 C. and holding them at this temperature for a certain period of time, where upon they will be cooled down very slowly. The lower the annealing temperature, the more time will be necessary for the annealing operation. Thus various ways will be given to impart to alloys of the stellite type a resistance to abrasion which is far superior to that heretofore known..

We claim:

1. A method of-producing hard alloys of the stellite type on the basis of cobalt, chromium, tungsten and not over 3.5% carbon, a part of which is present inthe form of graphite, consisting in forming the alloy by combining the requisite alloy components, casting the alloy thus formed and cooling with retarded velocity.

2. A method of producing hard alloys of the stellite type on the basis of cobalt, chromium, tungsten and carbon, a part of which 'is present in the form of graphite, consisting in forming the alloy by combining the requisite alloy components, casting the alloy in superheated condition so that slow solidification takes place.

3. A method of producing hard alloys of the stellite type on the basis of cobalt, chromium, tungsten and carbon, consisting in formingthe alloy by combining the requisite alloy components, casting the alloy, cooling the alloy and converting the carbon into graphite by heating the solidified alloy to aternperature above 7 00 C. and slowly cooling' the heated alloy.

4. Hard alloy of the stellite type based on the components cobalt, chromium, tungstem, and containing 2% to 3.5% carbon, the essential part of which is transformed into graphite by a method of the type known for transforming carbon into graphite in the manufacture of cast iron. I 5. Method of producing hard alloys of the stellite type on the basis of cobalt, chromium,

tungsten and carbon, comprising solidifying the alloys in the usual manner, obtaining the formation of graphite by heating the alloy thus solidified to a temperature of more than 700 C. and then cooling the alloy at a relatively slow rate.

ERNST HERMANN SCHULZ. KARL LOBBECKE. 

